Respiratory airways resistance measurements were made with the airflow perturbation device (APD) on swine, a mechanical analog, exercising subjects, and sedentary subjects with respiratory abnormalities. All data have not been analyzed, but APD measurements do underestimate airways resistance, with further underestimation as screen rotation frequency increases. Phase shift between mouth pressure and flow signals may be able to estimate airway compliance. Pulmonary function data, minute volume, respiratory quotient, oxygen uptake, airways resistance, and exhalation time for exercising subjects have been obtained and will be analyzed to determine if correlations exist.